Regeneration of caustic solutions containing mercaptans



United States Paterrt REGENERATION OF- CAUSTIC SOLUTIQNS: CON TAININ GMERCALPTANS Percy Hainsworth, Sunbury-on-Thames, England; assignor to The British Petroleum Company Limited- NoDravving. Application September.20, 1954 Serial No. 457,279.

Claims priority, application Great Britain:

September 24, 1953 8' Claims. (Cl.- 23.-18.4)

This, invention. relates to the regeneration of caustic. solutions containing mercaptans, such as those used'in the treatment of petroleum hydrocarbons for the removal of sulphur compounds therefrom.

From time to time it is necessary to regenerate the-mercaptan-containing caustic solution either by boiling out most of the mercaptans and burning them as was originally done or :by converting the mercaptans into disulphides which are insoluble in caustic solution and can be removeda an oxygen-containing gas, such as air, in the presence of an oxidation catalyst. Suitable catalysts comprise tannin and similar organic bodies which howeven, suifer. f

from the disadvantage that they are themselves converted by oxidation into a form in which they are no longer-effective as oxidation catalysts. In, the regeneration of mercaptan-containing caustic solutions therefore using. such oxidation catalysts, it is necessary to leave; a small proportion of the mer-captans unoxidised'si nce it has been found thatby this means the oxidation ofthe organic oxidation catalyst, isprevented. This means howeveriq that the regeneration of'the caustic solution cannot be taken to completion sothat the efiiciency of the. mercaptan extraction process is correspondingly reduced.

This disadvantage would be avoided if the regeneration of the. mercaptan-containing. caustic. solution could. be eifected by means of an oxygen containing gas alone, but with normal contacting methods,.the rate, of oxidation. that is, the percent wt. of mercaptan sulphur removed per. hour from the caustic solution, is too slow for this. method to be a practicable one. The principal object of the present invention is to enable. the regeneration of mereaptan-containing caustic. solutions to be efiected in the absence of an oxidation catalystjby means of'an oxygen-containing gas in a sufiiciently short period ofjtime to constitute an economical and practicable process. Another important object of the invention is.to .eflect the regeneration of the mercaptan-containing caustic solution at a temperature low enough to.prevent, discolourisationpf" the oil' after treatment with the regenerated solution.

'According to the present invention, the regeneration. of'mercaptan-containing caustic solutionsjs efiectedinthe absence of organic oxidation catalysts by. means of oxygenv or an oxygen-containing gas, such as air,. which; is introducedinto the, caustic solutionin the formpf extremely smallbubbles. I

The invention will hereinafterbe described with reference to the use of air as the oxidising gas.

The necessary dispersion ofthe air in the caustic solution may, be effected in various ways. Thus, the air may be fedtogether with the,caustic solution to the suction sideofiacentrifugal' pump. A'gaimthe air may befed into the centre of a high speed stirrer rotating in the caustic solution. Yetagain, the air may be. fed "into the 2,844,440 Patented July 22, 1958 causticsolution via asintered. metal distributor. Thus, in experiments carried-out. it wasfound; that a stainless steel sinter having adiameterof 1.25" andiathickness of My" was sufiicient to regenerate 40,0/800 ml. of solution per hour in a column of about 185' in height. Under these conditions the sintered} metal; distributor had a back pressure of about 2 p. s. i. and required only occasional cleaning, forexample by immersion in dilute phosphoric: acid.

Theimprovementbrought about by-the.-.-dispersion of'the air. in the caustic. solutionin the form: ofextremely small: bubbles is illustrated by. the data set o ut in thefollowin'g. table.

. Oxygen- Mercap- Pore Tannin, Temper,- Utilisatan- Method of air diameter; percent ature, tion, Sulphur dispersion microns wt. F. percent Removal,

vol. percent wt./hr.

(1) H glass sinter 15-40 .4 145 27 .22 (2) H1 glass sinter 901-150 .45 i 140 11 11 (3) Gooch crucibles. 1, 000 .40 140 3' .02

(4) High speed 5 mixer nil 62-158 30 9 (5).. Centrifugal pump; nil i 135 41 l1 (6) Mild steel Sinter nil f 130 30., .05. (7) }steel pipe 3; 200 nil l 130 01.

It will; be. seen that satisfactory oxidation: rates: and: oxygen utilisations were obtainedin the absence of tannin inthe case of methods of'aii' dispersion Nos. 4-6 in all of whichthe air ispresentin-thetorm of: extremely.- small bubbles. With fur.ther reference to.the foregoing ;table: and particularly withreference. to] the cases. of air dis.-

7 persion Nos. 1.-3 wherein tannin is present as anwoxidizeing agent, the oxidation rate i.. e., the, speed at which mercaptansulphur is removed, issatisfactory, for. coma mercial purposes at .22% wt./hr. and. .l.l% wt./hr; in; the cases Nos. 1. and,2,. and. is. to.o low. for commercial purposes at .02%' wt./,hr.,.in. the. casev No. 3.. In the cases. o,f air dispersion Nos- 4 and. 5. whereintannin .v asoxidi'zing agent is absent,. the. oxidationv rates; of .9.%.- wt./hr.. and .1.1 wt./hr., respectively, areclearly commercially satisfactory,. and the. oxidation. rate. of. 0.05%." wt./hr., in. the, case NQ; 6,.though; low, isstill twoand. ahalfjtimeshigher than the-rate in thecaseNo. 3iand is. just adequate. for? commercial purposes. It. will... be. observedgthatin the casezNo.,6.the.pore..diameter of the.

metal. sinteli, as. a. measure. of. the. bubble. size,, is. 10;

mierons, whereas, in. the. cases. 4. and- 5.,. whichv result: in igher. oxidation rates, the. bubblesize; is certainly. very, much. less. than that. .obtainedlusing. a. sinter. having, a... pore size of, 10. microns,,heing, so small. as to .be..impos=\ sible ofmeasuremenh.

at room temperature il e. 60/8.Q E.,,.in.order,to avoid-,.

the colour formation experienced at 140 F. As: there was; no, tannin. p resent the.v solution was, regenerated to the lowest percentage of. mercaptan; sulphur. attainable.

under the conditions. employed, il eat F. or. 1.40.- R1,. minutes residence time andaiigrateahout. 10.0.:mhl. minute. or. 2400' cu. ft./ 10.0.0v gallons. ofjsolutizer. solution. The results set outin the. followingTf-ableNQ. 1. show. that,

v the regenerated solutizer. solution was almost as. efiective.

as. fresh solution.

A 3 Na Table 1 microns at a gas rate and in an amount suflicient to efliect an oxidation rate of at least about 0.05 Wt. per Mercaptan Sulphur Content, percent by wt. hour of mercaptan Sulphur F Tempe]?- 2. In the method of regenerating a mercaptan-conature of Heayy Regen. In solutizer In on In 011mm 5 taming caustic alkah solution by contacting the solution Benlme g E a in the absence of an organic oxidation catalyst with an F- tion with Bef After B f After Fresh oxldizing gas selected from the class consisting of an Resell Regen EXtMOtEXtYM-t solutizer and oxygen, the improvement which comprises, introducing the gas into the solution in the form of bubbles .013 .002 Kuwait m 002 W 006 I 005 10 at least as small as the bubbles produced by passing said m3 gas through a metal sinter havmg a pore diameter of 140 1124 microns, said gas being introduced into the solution Qatar 053 003 m1 by passage through a metal sinter disposed in said solu- Agha 80 427 1143 tion at a gas rate and in an amount sufiicient to effect an oxidation rate of at least about 0.05% wt. per hour Iraq and Qatar stabilised gasolmes, after extraction of mercaptan sulphur removed. w th solutizer solution regenerated at 140 F, became 3. In the method of regenerating a mercaptan-com highly coloured. The colour was reduced by frequent taining caustic alkali solution by contacting the solution changes of wash oil or by water washing the extracted in the absence of an organic oxidation catalyst with an heavy benzine. No such colour formation occurred when oxidizing gas selected from the class consisting of air and solutizer was regenerated at 80 F. The results are set out in the following Table No. 2.

oxygen, the improvement which comprises, introducing the gas into the solution in the form of bubbles at least Referring to the above table, the colour of the oils, after treatment with solutizer solution regenerated at 140 F., would have been bad if the wash oil had not been changed frequently and if the treated oils had not been vigorously water washed by hand. No such precautions were taken with the oils treated with solutizer solution regenerated at 80 F.

The advantages to be gained by the use in the solutizer process of an air distributor so elfective that regeneration of the spent solutizer solution is adequate without recourse to tannin and heating are:

(1) The regeneration of the solutizer solution can be carried as near as practicable to completion to produce a solution about as effective as fresh solutizer solution.

('2) The possible applications of the solutizer process are extended since in addition to using regenerated solutizer solution for butanes and light gasolines, they can be used effectively to remove less soluble mercaptans.

(3) A lower extraction temperature may be used without taking special steps to that end. In the tannin solutizer process, the regenerated solution is not usually cooled to the ambient temperature although better extraction occurs at lower temperatures.

(4) A lower regeneration temperature is possible thus saving steam and in some cases eliminating the necessity for the use of cupro nickel.

(5) The solutizer process is simpler to control since no determination of tannin content and few determinations of mercaptan sulphur content of regenerated solutizer solutions are required.

I claim:

1. In the method of regenerating a mercaptan-containing caustic alkali solution by contacting the solution in the absence of an organic oxidation catalyst with an oxidizing gas selected from the class consisting of air and oxygen, the improvement which comprises, introducing the gas into the solution in the form of bubbles at least as small as the bubbles produced by passing said gas through a metal sinter having a pore diameter of 10 as small as the bubbles produced by passing said gas through a metal sinter having a pore diameter of 10 40 microns, by feeding said gas together with said solution to the suction side of a centrifugal pump at a gas rate and in an amount sufficient to effect an oxidation rate of at least about 0.05%. wt. per hour of mercaptan sulphur removed.

4. In the method of regenerating a mercaptan-containing caustic alkali solution by contacting the solution in the absence of an organic oxidation catalyst with an oxidizing gas selected from the class consisting of air and oxygen, the improvement which comprises, introducing the gas into the solution in the form of bubbles at least as small as the bubbles produced by passing said gas through a metal sinter having a pore diameter of 10 microns, by feeding said gas into the center of a high speed stirrer rotating in said solution at a gas rate and in an amount sufficient to eifect an oxidation rate of at least about 0.05% wt. per hour of mercaptan sulphur removed.

5. In the method of regenerating a mercaptan-containing caustic alkali solution by contacting the solution in the absence of an organic oxidation catalyst with an oxidizing gas selected from the class consisting of oxygen and air, the improvement which comprises, introducing the gas into the solution in the form of bubbles at least as small as the bubbles produced by passing said gas through a sintered metal distributor having a pore di- 7 the gas into the solution in the form of bubbles at least,

as small as the bubbles produced by passing said gas through a sintered metal distributor having a pore diameter of microns at a gas rate and in an amount suflicient to efiect an oxidation rate of at least about 0.05% Wt. per hour of mercaptan sulphur removed, the solution being at a temperature of 60 to 80 F.

7. In the method of regenerating a mercaptan-containing caustic alkali solution by contacting the solution in the absence of an organic oxidation catalyst with an oxidizing gas selected from the class consisting of oxygen and air, the improvement which comprises, introducing the gas into the solution in the form of bubbles at least as small as the bubbles produced by passing said gas through a sintered metal distributor having a pore diameter of 10 microns, said gas being introduced into the solution by passage through a sintered metal distributor disposed in said solution and having a pore diameter of 10 microns at a gas rate and in an amount suflicient to efiect an oxidation rate of at least about 0.05% Wt. per hour of mercaptan sulphur removed, and the solution being at atmospheric temperature.

8. In the method of regenerating a mercaptan-containing caustic alkali solution by contacting the solution in the absence of an organic oxidation catalyst with an oxidizing gas selected from the class consisting of oxygen and air, the improvement which comprises, introducing the gas into the solution in the form of bubbles at least as small as the bubbles produced by passingsaid gas through a sintered metal distributor having a pore diameter of 10 microns, said gas being introduced at a gas rate and in an amount sufficient to efiect an oxidation rate of at least about 0.05% wt. per hour of mercaptan sulphur removed through a sintered metal distributor disposed in the solution and having under the conditions a back pressure of 2 p. s. i., and the solution being at a temperature of to F.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN THE METHOD OF REGENERATING A MERCAPTAN-CONTAINING CAUSTIC ALKALI SOLUTION BY CONTACTING THE SOLUTION IN THE ABSENCE OF AN ORGANIC OXILDATION CATALYST WITH AN OXIDILZING GAS SELECTED FROM THE GLASS CONSISTING OF AIR AND OXYGEN, THE IMPROVEMENT WHICH COMPRISES, INTRODUCING THE GAS INTO THE SOLUTION IN THE FORM OF BUBBLES AT LEAST AS SMALL AS THE BUBBLES PRODUCED BY PASSING SAID GAS THROUGH A METAL SINTER HAVING A PORE DIAMETER OF 10 MICRONS AT A GAS RATE AND IN AN AMOUNT SUFFICIENT TO EFFECT AN OXIDATION RATE OF AT LEAST ABOUT 0.05% WT. PER HOUR OF MERCAPTAN SULPHUR REMOVED. 